The present invention relates generally to a screen printing machine, and more particularly to a screen printing machine having novel adjusting arrangements.
It is known to provide screen printing machines in which an endless printing screen travels about rollers, two of which have their axes of rotation located in a common horizontal plane so that the printing screen forms a printing run between these two rollers, that is a run in which printing takes place through the printing screen upon an underlying workpiece. This type of screen printing machine has certain disadvantages, including the most important one that if the workpiece becomes displaced transversely of the printing screen, that is axially of the rollers around which the printing screen is guided, there will no longer be any proper registry between the printing screen and the workpiece. Conversely, it is also known that quite frequently the printing screen itself will shift axially of the rollers with reference to the workpiece, leading to the same difficulties. In order to avoid this problem the two rollers between which the printing run is formed must be readjusted every time such a displacement of the printing screen and/or the workpiece occurs. This is particularly disadvantageous in the case of multi-pass printing, that is in case of multicolor printing or the like. Evidently, if one part of a pattern or the like has been printed onto a workpiece, and another part is to be overprinted, there must be precise registry between printing screen and workpiece because otherwise overlapping of the colors will occur, or other difficulties may arise from this lack of registry. The difficulty mentioned above arises from the fact that every time the rollers are readjusted, the printing screen itself, or at least that portion constituting the printing run, will shift with reference to the workpiece. Moreover, since the printing screen is located in the printing run directly on the workpiece, any shifting between printing screen and workpiece is disadvantageous, especially in the case of workpieces--such as rugs, carpets and the like--having a nap, because any relative displacement between printing screen and workpiece results in disturbing of the nap and thus in printing imperfections.